1. Field of the Invention
The invention concerns polymers which form compatible (miscible) polymer mixtures (polymer blends), specifically of a polymer P1 containing styrene as the monomer, and a polymer P2 containing a heterocyclic group with 5-8 ring atoms and at least 2 hetero atoms in the ring, and objects made of these polymers, where one of the polymers forms a coating on the other polymer or on the polymer blend, e.g. a coating on the compatible polymer mixtures.
2. Discussion of the Background
As a rule, different polymer species are considered to be incompatible with one another, i.e. different polymer species generally do not form a homogeneous phase, which would be characterized by complete miscibility of the components, down to small amounts of a component.
Certain exceptions to this rule have caused increasing interest, particularly among the experts concerned with the theoretical interpretation of the phenomena. Completely compatible mixtures of polymers demonstrate complete solubility (miscibility) in all mixture ratios.
A summary representation of miscible polymer systems can be found, for example, in D.R. Paul et al., Polymer and Engineering Science, 18 (16) 1225-34 (1978); J. Macromol. Sci. Rev. Macromol. Chem. C., 18 (1), 109-168 (1980).
As evidence of the miscibility, the glass temperature Tg or the so-called "optical method", i.e., the clarity of a film poured from a homogeneous solution of the polymer mixture, was often used as a reference. (See Brandrup-Immergut, Polymer Handbook, Ed., III, 211-2113). As a further test for the miscibility of polymers which are different from one another, the occurrence of the lower critical solution temperature (LCST) is used. (See DE-A 34 36 476.5 and DE-A 34 36 477.3). The occurrence of the LCST is based on the process which occurs during warming, where the polymer mixture, which has been clear and homogeneous until then, separates into phases and becomes optically cloudy to opaque. This behavior is a clear indication, according to the literature, that the original polymer mixture had consisted of a single homogeneous phase which was in equilibrium. Examples of existing miscibility are represented, for example, by the systems polyvinylidene fluoride with polymethyl methacrylate (PMMA) or with polyethyl methacrylate. (U.S. Pat. Nos. 3,253,060, 3,458,391, and 3,459,843). Recent results concerning "polymer blends" and possible applications for them are reported by L.M. Robeson (Polym. Engineering & Science, 24 (8), 587-597 (1984)).
Copolymers of styrene and maleic acid anhydride, as well as of styrene and acrylonitrile are compatible with polymethyl methacrylate (PMMA) under certain conditions (DE-A 20 24 940). The improved properties of molding materials of these types are emphasized. In the same way, copolymers of styrene and monomers which contain hydroxyl groups which can form hydrogen bonds are also compatible with polymethacrylates in certain compositions, for example copolymers of styrene and p(-2-hydroxyhexafluoroisopropyl) styrene (B.Y. Min and Eli M. Pearce, Organic Coatings and Plastics Chemistry, 45, (1981) 58-64), or copolymers of styrene and allyl alcohol (F. Cangelosi and M.T. Shaw, Polymer Preprints (Am. Chem. Soc., Div. Polym. Chem.) 24, (1983), 258-259). Compatibility was also found in the system of acrylonitrile copolymers mixed with poly(tetrahydrofurfuryl methacrylate) (Goh, S.H., Siow, K.S., J. Appl. Polym. Sci., (1987), 33(5) 1949). In the same way, polytetrahydrofurfuryl methacrylate is compatible with copolymers of styrene and allyl alcohol (Goh, S.H., Polym. Bull., (1987), 17(3), 221-4). Compatibility is also found for acrylonitrile/styrene copolymers, i.e. acrylonitrile/ .alpha.-methyl styrene copolymers with polymethyl methacrylates which contain sterically hindred amino groups. For example, a methyl methacrylate/2,2,6,6-tetramethyl piperidinyl methacrylate copolymer is compatible with these styrene/acrylonitrile or .alpha.-styrene/acrylonitrile copolymers. (Goh et al., J. Appl. Polym. Sci., (1986), 31, 2055).
Compatibility is also found for mixtures of polyp-vinyl phenol and polymethacrylates. For example, poly-p-vinyl phenol is compatible with polymethyl methacrylate, polyethyl methacrylate, polypropyl methacrylate or polytetrahydrofurfuryl methacrylate. (Goh, S.H., Siow, K.S., Polym. Bull., (1987), 17(5), 453-8).
Polystyrene itself, as well as other polymers which contain styrene, are considered to be incompatible with polymethyl methacrylate. For example, M.T. Shaw and R.H. Somani indicate a miscibility with polystyrene of only 3.4 ppm (PMMA with a molecular weight of 160,000) or 7.5 ppm (PMMA with a molecular weight of 75,000) (Adv. Chem. Ser., (1984), 206 (Polym. Blends Compos. Multiphase Syst.), 33-42; CA 101 : 73417e). Even polystyrene with a very low molecular weight has little compatibility with PMMA. For example, a mixture of 20% of a styrene oligomer with an extremely low molecular weight (MW : 3,100) already does not yield a clear product any more. At a molecular weight of 9,600, which is also still very low, even a solution of only 5 % in PMMA is only translucent. (Raymond R. Parent and Edward V. Tompson, Journal of Polymer Science: Polymer Physics Edition, Vol 16, 1829-1847 (1978)). Other polymethacrylates and polyacrylates demonstrate just as little miscibility with polystyrene to form transparent plastics. This is true, for example, for polyethyl methacrylate, polybutyl methacrylate, polyisobutyl methacrylate, polyneopentyl methacrylate, polyhexyl methacrylate and many others. See also R.H. Somani and M.T. Shaw, Macromolecules 14, 1549-1554 (1981).
In contrast, mixtures of polystyrene and polycyclohexyl acrylate and mixtures of polystyrene and polycyclohexyl methacrylate are completely compatible. (see German patent application P 36 32 369.1 filed 9/24/86). The compatibility is so good that when these mixtures are heated, an LCST does not occur, i.e. the compatibility exists over the entire accessible temperature range. This good polystyrene compatibility no longer exists for heavily substituted cyclohexyl derivatives. Compatibility with polystyrene is found neither for poly-3,3,5-trimethylcyclohexyl methacrylate nor for polyisobornyl methacrylate. In comparison, the compatibility of poly-.alpha.-methyl styrene with polymethacrylates is better (see also German patent application P 36 32 370.5).
Mechanical mixtures of polymers (polyblends) have resulted in plastic products with improved properties in certain cases and in certain areas of the plastics industry (See Kirk-Othmer 3rd edition, Vol. 18, pp. 443-478, J. Wiley (1982)). The physical properties of such "polyblends" generally represent a compromise, which can mean an overall improvement as compared with the properties of the individual polymers. In these situations, multi-phase polymer mixture have achieved much greater commercial significance than compatible miscible mixtures (See Kirk-Othmer, loc. cit., p. 449).
Multi-phase and compatible miscible mixtures must therefore be considered separately with regard to both their physical properties and their properties which are relevant for application technology, especially their optical properties (transparency, clarity, etc.). As already explained, a lack of compatibility often sets narrow limits for mixing plastics with the goal of achieving an improved overall spectrum of properties.